1. Field
The present disclosure generally relates to an over voltage surge protection circuit. More particularly, the present disclosure relates to a rail surge voltage protector applied to railway tracks in the rail industry, providing lower residual voltage than gas discharge tubes commonly used in the rail industry.
2. Description of the Related Art
The railway industry uses electrical signals to help monitor and manage railway traffic. For example, a track circuit may be attached to the rails of a train track to electrically determine the presence of a train on the train track, such as its speed and location. The track circuit allows railway signaling systems to semi-automatically display traffic signals, which includes signals to slow down or stop for an occupied track such as rail crossing arms or to signal other unsafe conditions, and signals to switch tracks.
Because the tracks may be electrified, surge or over voltage protection is required to protect attached track circuits. A rail surge voltage protector provides means of surge protection. The rail surge voltage protector must also provide failsafe self-detection and disconnection in case of a catastrophic short circuit surge component failure in order to prevent erroneous track switching function. The rail surge voltage protector cannot interfere with or be affected by other rail circuit operations, such as audio frequency range signal generation, parallel relay activation functions, immunity to high voltage wave shapes which appear across rails, extraneous noise levels from power line coupling and potential short circuit or partial short conditions occurring across the rails, yet must still be able to detect its own surge components in case of shorts. A modular rail surge voltage protector would more easily be installed with standard rail buss connections. The rail surge voltage protector would also have a terminal connection or path to earth ground.
In addition, the rail surge voltage protector must not add alien signals or otherwise interfere with normal rail signals or operating voltages mandating high impedance/resistance passive circuits for detection. For example, one typical application may provide a 12Vdc nominal at 15 mA. Typically, a 4Vpk-pk 100 Hz to 20 kHz square wave at 500 mA is applied across the rails in the proximity of a train.
The disconnect relay mechanism must mechanically disconnect the entire circuit from the rails once the disconnect scheme is triggered by a follow-on track signal. The disconnect relay mechanism must have the mechanical advantage to overcome or disengage any contact spot welding that may occur during a catastrophic surge event. The surge components and disconnect relay contacts must be robust enough to handle 15kA 8 us/20 us surge currents, operating at −25 degrees C. to +85 degrees C.